The purpose of this research is to elucidate some of the factors which control the shedding of the rod outer segment discs and their subsequent phagocytosis by the pigment epithelium (PE). It is hoped that when the process of phagocytosis is more fully understood, this may lead to a greater understanding of degenerative diseases of the retina, such as retinitis pigmentosa. In all of the experiments proposed in this project, the effect of various lighting conditions will be studied in normal and, in appropriate cases, dystrophic animals. In the first class of experiments, phagocytosis will be assayed by phagosome counts under the light microscope. Undisturbed animals will be used as well as animals having one eye occluded and animals which have had surgical alteration of various pathways in the visual tract or neuroendocrine system. Organ cultures of the retina-PE unit will further test the localization of the control of phagocytosis. In addition to phagosome counts, radioactively labeled retinas can be incubated with PE so that phagocytosis can be assayed by radioactivity in washed PE cells. This in vitro system will also be used to investigate the effects of various biochemical agents such as melatonin, TRH, metabolic inhibitors, beta-adrenergic agonists and antagonists on phagocytosis. In the next class of experiments, changes in the composition of the outer segment membranes will be assayed by two methods. Autoradiography of sugar and lipid moieties will be performed, as well as an electron microscope histochemical study of lectin binding sites. Finally, biochemical techniques will be used. N-acetyltransferase and HIOMT enzyme levels of the retina will be measured, as well as the lipid composition of the outer segment membranes.